It's OK to________an electrical appliance on so long as you are using it.
A．leave B．make
C．turn D．open
It________heavily for 2 weeks and the farmers were very worried.
A．has been raining B．had been raining
C．has rained D．had been rained
You cannot tell________looking at someone whether or not he has HIV.
A．without B．by
C．for D．with
The days are gone________you can breathe fresh，unpolluted air or drink clean, unpolluted water in the countryside.
A．when B．that
C．where D．which
Learn some relaxation exercises and do them every time you feel________.
A．embarrassed B．stressed
C．ashamed D．impressed
Many young people don't work hard, and regret it later when the opportunity is gone.They only realize it________it is too late.
A．when B．before
C．in case D．until
